Fish In China Research Articles

Characterization, Expression, and Functional Analysis of the Northern Snakehead (Channa argus) Hepcidin.

Hepcidin, an antimicrobial peptide (AMP), is a well-conserved molecule present in various species such as fish, amphibians, birds, reptiles, and mammals. It exhibits broad-spectrum antimicrobial activity and holds a significant role in the innate immune system of host organisms. The northern snakehead (Channa argus) has become a valuable freshwater fish in China and Asia. In this investigation, the cDNA encoding the hepcidin gene of northern snakehead was cloned and named caHep. The amino acid sequences and protein structure of caHep are similar to those of hepcidins from other fish. The eukaryotic expression product of the caHep gene showed broad-spectrum antibacterial activity. Scanning electron microscope analysis indicated that the caHep peptide inhibited bacterial growth by damaging their cell membranes. Lipopolysaccharide (LPS) injection induced significant expression of caHep, implying the involvement of caHep in the innate immune response of northern snakeheads. This investigation showed that the caHep peptide is potentially a robust antibacterial drug against bacterial diseases in aquaculture animals.

Transcriptomic analysis of large yellow croaker (Larimichthys crocea) reveals the suppression of the inflammatory response from Cryptocaryon irritans infection

Large yellow croaker (Larimichthys crocea) is the most productive marine fish in China. Cryptocaryon irritans is an extremely destructive parasite that causes great economic losses in large yellow croaker aquaculture industry. Therefore, it is very necessary to study the immune response of large yellow croaker in response to C. irritans infection. In this study, the transcriptomic profiles of large yellow croaker were sequenced and analyzed in the brain and head kidney at 72 h after C. irritans infection. Cytokines and chemokines related terms were significantly enriched based on the GO enrichment of down-regulated differentially expressed genes (DEGs) from the head kidney. Meanwhile, cytokine-cytokine receptor interaction was significantly enriched based on the KEGG enrichment of up-regulated DEGs from the brain and down-regulated DEGs from the head kidney, respectively. Moreover, the majority of inflammation-related DEGs were significantly up-regulated in the brain, but distinctly down-regulated in the head kidney. These results showed that the brain and head kidney might play different roles against C. irritans infection, and the inflammatory response of large yellow croaker may be restrained during C. irritans infection. Taken together, the transcriptomic analyses will be helpful to more comprehensively understand the immune mechanism of teleost against C. irritans infection, and provide a theoretical basis for the prevention and treatment of Cryptosporidiosis.

Four new hypogean species of the genus Triplophysa (Osteichthyes, Cypriniformes, Nemacheilidae) from Guizhou Province, Southwest China, based on molecular and morphological data

Recently described cave species of the genus Triplophysa have been discovered in southwestern China, suggesting that the diversity of the genus is severely underestimated and that there may be many undescribed species. In this work, four new species of the genus Triplophysa are described from southwestern Guizhou Province, China, namely Triplophysa cehengensis Luo, Mao, Zhao, Xiao & Zhou, sp. nov. and Triplophysa rongduensis Mao, Zhao, Yu, Xiao & Zhou, sp. nov. from Rongdu Town, Ceheng County, Guizhou, Triplophysa panzhouensis Yu, Luo, Lan, Xiao & Zhou, sp. nov. from Hongguo Town, Panzhou City, Guizhou, and Triplophysa anlongensis Song, Luo, Lan, Zhao, Xiao & Zhou, sp. nov. from Xinglong Town, Anlong County, Guizhou. These four new species can be distinguished from all recognized congeners by a combination of morphological characteristics and significant genetic divergences. The discovery of these species increases the number of known cave species within the genus Triplophysa to 39, making the genus the second most diverse group of cave fishes in China after the golden-line fish genus Sinocyclocheilus. Based on the non-monophyletic relationships of the different watershed systems in the phylogenetic tree, this study also discusses the use of cave species of the genus Triplophysa to determine the possible historical connectivity of river systems.

Depuration and Starvation Regulate Metabolism and Improve Flesh Quality of Yellow Catfish (Pelteobagrus fulvidraco).

Fat deposition and off-flavor in the muscle are the main problems affecting flesh quality in aquaculture fish, especially in catfish, leading to low acceptability and reduced market price. Yellow catfish is an important aquaculture fish in China. In this study, 40 days of depuration and starvation treatment were explored to improve the muscle quality of aquaculture yellow catfish. After depuration and starvation, the body weight, condition factor (CF) and mesenteric fat index (MFI) were all significantly decreased 20 days after treatment. The metabolomic profiles in muscle were characterized to analyze the muscle quality in yellow catfish. The results showed that the content of ADP, AMP, IMP, glutamic acid and taurine were significantly increased between 20 and 40 days post-treatment in the muscle of yellow catfish during the treatment, which was positively associated with the flesh tenderness and quality. In contrast, aldehydes and ketones associated with off-flavors and corticosterone associated with bitter taste were all decreased at 20 days post-treatment. Considering the balance of body weight loss and flesh quality improvement, depuration and starvation for around 20 days is suitable for aquaculture yellow catfish. Our study not only provides an effective method to improve the flesh quality of aquaculture yellow catfish but also reveals the potential mechanism in this process.

Nile tilapia TBK1 interacts with STING and TRAF3 and is involved in the IFN-β pathway in the immune response

Nile tilapia (Oreochromis niloticus) occupies an important position in the culture of economic fish in China. However, the high mortality caused by streptococcal disease has had a significant impact on the tilapia farming industry. Therefore, it is necessary to clarify the immune mechanism of tilapia in response to Streptococcus agalactiae. As a hub in the natural immune signaling pathway, the junction molecule can help the organism defend against and clear pathogens and is crucial in the signaling pathway. In this study, the cDNA sequence of Nile tilapia TBK1 was cloned, and the expression profile was examined in normal fish and challenged fish. The cDNA sequence of the TBK1 gene was 3378 bp, and its open reading frame (ORF) was 2172 bp, encoding 723 amino acids. The deduced TBK1 protein contained an S_TKc domain, a coiled coil domain and a ubiquitin-like domain (ULD). TBK1 had the highest homology with zebra mbuna (Maylandia zebra) and Lake Malawi cichlid fish (Astatotilapia calliptera), both at 97.59%. In the phylogenetic tree, TBK1 forms a large branch with other scleractinian fish. TBK1 expression was highest in the brain and lowest in the liver. LPS, Poly I:C, and S. agalactiae challenge resulted in significant changes in TBK1 expression in the tissues examined. The subcellular localization showed that TBK1-GFP was distributed in the cytoplasm and could significantly increase IFN-β activation. Pull-down results showed that there was an interaction between TBK1 and TRAF3 and an interaction between STING protein and TBK1 protein. The above results provide a basis for further investigation into the mechanism of TBK1 involvement in the signaling pathway.

Genome-wide DNA methylation mediates the resistance to vibriosis in Cynoglossus semilaevis

Chinese tongue sole (Cynoglossus semilaevis) is an economically important marine fish in China. However, vibriosis has caused huge mortality and economic losses in its culturing industry. To reveal the effect of DNA methylation on the resistance to vibriosis in tongue sole, we conducted RNA sequencing and whole genome bisulfite sequencing (WGBS), and compared the gene expressions and DNA methylation patterns between the resistant and susceptible families. We identified a total of 741 significantly differentially expressed genes (DEGs) in kidney and 17460 differentially methylated genes (DMGs), which were both enriched in immune-related pathways, such as “cAMP signaling pathway” and “NOD-like receptor signaling pathway”. Through the correlation analysis of DEGs and DMGs, we identified two important immune pathways, including “complement and coagulation cascades”, and “cytokine-cytokine receptor interaction”, which played important roles in regulating the inflammation level and immune homeostasis. For example, the expression of proinflammatory cytokine il17c was down-regulated under the regulation of DNA methylation; in addition, the expression of protease-activated receptor 3 (par3) was up-regulated, which could induce the up-expressionof il8. These results demonstrated that the regulation of DNA methylation on the genes involved in immune responses might contribute to the resistance to vibriosis in tongue sole, and provided a basis for the control of diseases in fish aquaculture.

Molecular Identification and Expression Analysis of an Intelectin Gene in the Yellow Catfish Pelteobagrus fulvidraco (Siluriformes: Bagridae)

Intelectins (ITLNs) are a family of calcium-dependent lectins with carbohydrate-binding capacity, are distributed across various vertebrates, and play an important role in the innate immune response against pathogen infection. The yellow catfish Pelteobagrus fulvidraco (Siluriformes: Bagridae) is an economically important fish in China. The aim of this study was to quantify the gene expression of ITLN in response to pathogen-associated molecular patterns (PAMPs) stimulation. Here, the ITLN gene of P. fulvidraco was characterized and named PfITLN. The full-length cDNA of PfITLN was 1132 bp, including a 5’-untranslated region (UTR) of 140 bp, a 3’-UTR of 110 bp, and an open reading frame (ORF) of 882 bp encoding a polypeptide of 293 amino acids, which contains a signal peptide and two fibrinogen-related domains (FReDs). PfITLN had a molecular weight of 32.39 kDa with a theoretical pI of 5.03. The deduced PfITLN amino acid sequence had 81%, 64%, and 55% homology with Ictalurus furcatus, Danio rerio, and Homo sapiens, respectively. Moreover, the predicted tertiary protein structure of PfITLN was highly similar to that of other animals, and phylogenetic analysis showed that the PfITLN protein was close to those of other Teleostei. Real-time quantitative reverse transcription-PCR (qRT-PCR) analysis showed PfITLN expression in all examined tissues, with the highest abundance seen in the liver, followed by the head kidney, spleen, trunk kidney, and muscle. After PAMP infection with lipopolysaccharide (LPS) and polyriboinosinic polyribocytidylic acid (poly I:C), the expression levels of PfITLN were significantly upregulated at different time points. These results suggested that PfITLN might be involved in innate immunity.

Identification of circRNAs and circRNA-mRNA network of Epinephelus coioides during Singapore grouper iridovirus infection

Circular RNA (circRNA), one of the important non-coding RNA molecules with a closed-loop structure, plays a key regulatory role in cell processing. In this study, circRNAs of Epinephelus coioides, an important marine cultured fish in China, were isolated and characterized, and the network of circRNAs and mRNA was explored during Singapore grouper iridovirus (SGIV) infection, one of the most important double stranded DNA virus pathogens of marine fish. 10 g of raw data was obtained by high-throughput sequencing, and 2599 circRNAs were classified. During SGIV infection, 123 and 37 circRNAs occurred differential expression in spleen and spleen cells, indicating that circRNAs would be involved in the viral infection. GO annotation and KEGG demonstrated that circRNAs could target E. coioides genes to regulate cell activity and the activation of immune factors. The results provide some insights into the circRNAs mediated immune regulatory network during bony fish virus infection.

The heat shock protein 20 gene family in large yellow croaker (Larimichthys crocea): Identification, phylogenetic relationships, expression analyses

Large yellow croaker (Larimichthys crocea) is an economically important fish in China, but its aquaculture industry has been threatened by both biotic and abiotic stressors such as hypoxia and pathogens. In the current study, hsp20 genes were identified and analyzed systematically for the first time from the genome of large yellow croaker, and their roles in hypoxia response and Aeromonas hydrophila, Pseudomonas plecoglossicida infection were investigated. Herein, 11 hsp20 genes were identified and annotated, phylogenetic analysis and selection pressure analysis showed that the hsp20 genes were evolutionarily-constrained and their function was conserved among fishes. Besides, we observed the expression patterns of the hsp20 genes under hypoxia and two pathogens’ stress. In brief, seven, four, seven genes responded to hypoxia stress, A. hydrophila infection and P. plecoglossicida challenge, respectively, which indicated that they were involved in hypoxia and disease responses. Furthermore, pathogen- and time-specific pattern was observed after A. hydrophila and P. plecoglossicida infection whereas tissue-specific pattern was observed after hypoxia exposure, revealing that hsp20 genes showed differential functions in response to hypoxia and immune stress. Taken together, these results provided preliminary information for future analysis of the roles of hsp20 genes in both biotic and abiotic stress response in fish.

The first detection of Myxobolus lentisuturalis Dyková, Fiala et Nie, 2002, a highly pathogenic muscle-infecting parasite of gibel carp (Carassius auratus gibelio Berg, 1932) in Hungary.

Myxobolus lentisuturalis is a myxosporean parasite infecting the musculature both of goldfish (Carassius auratus auratus) and gibel carp (Carassius auratus gibelio). The species was originally described in China from gibel carp that is a common fish for sport fishing in Hungary meanwhile is one of the most popular farmed fish in China due to its high demand. Eighteen gibel carp with distortions were collected from a barrage pond in southern Hungary. All fish had large humps in the dorsolateral region due to infection of the muscle between the head and the dorsal fin. The swollen degenerated tissue was filled with myxozoan spores, which were collected for morphological and molecular studies. By size and morphology, the spores were consistent with morphological description of M. lentisuturalis. Histopathological examination showed that the formation of plasmodia containing myxospores leads to severe destruction of muscle tissue. The 18S ribosomal DNA and 28S ribosomal DNA data of the samples presented matched with previous sequences of M. lentisuturalis in GenBank. Phylogenetic analyses confirmed that our sequences belong to a monophyletic group with them supported by a high bootstrap. This study highlights the occurrence of a highly pathogenic myxozoan, M. lentisuturalis in Hungary as a new geographical location.

Identification of long non-coding RNA MSTRG.5748.1 and MSTRG.7894.1 from Megalobrama amblycephala and their potential roles in innate immunity.

Megalobrama amblycephala is one of the most economically important freshwater fish in China, and the bacterial septicemia caused by Aeromonas hydrophila is a serious threat to the breeding industry of M. amblycephala. Unfortunately, the characterization of long noncoding RNA (lncRNA) in response to A. hydrophila infection has not been performed in M. amblycephala. To better understand the biological significance of lncRNA in the immune system, we identified two lncRNA, named MSTRG.5748.1 and MSTRG.7894.1, as playing critical roles in the antibacterial response of M. amblycephala. After separating the nucleus and cytoplasm of the hepatocytes from M. amblycephala, cellular localization of MSTRG.5748.1 and MSTRG.7894.1 was performed to predict their functions. The results showed that MSTRG.5748.1 was mainly expressed in the nucleus, suggesting that its functions are mostly to regulate the expression of downstream genes through epistasis and transcription. MSTRG.7894.1 existed in both the nucleus and cytoplasm, which indicated that it has many regulatory modes. qPCR analysis showed that MSTRG.5748.1 and MSTRG.7894.1 were expressed in the immune-related organs of M. amblycephala, and significantly changed in the liver after A. hydrophila infection. RNA-seq analysis revealed that differentially expressed genes (DEGs) were mainly enriched in antigen processing and presentation via MHC class I, RIG-I-like receptor (RLR) signaling pathway, and IFN-related pathway, and a large number of pathway-related genes were significantly regulated after lncRNA overexpression in muscle cell of M. amblycephala. Overexpression of MSTRG.5748.1 and MSTRG.7894.1 significantly inhibited the expression of STING and IFN, significantly upregulated muscle cell viability, and promoted cell proliferation by targeting STING and IFN.

Heavy metal contamination risk assessment of commercial fish in China's Dongting Lake

Rapid urbanization, industrialization, and intense agricultural practices in the cities and communities along the rivers have resulted in potentially toxic elements, such as heavy metals, being released into the river water and subsequently deposited into Dongting Lake, thereby posing a severe threat to fish, invertebrates, and humans. In this work, eight fish species, representing different kinds of feeding habits and living habitats, were collected from Dongting Lake, China. The concentration of heavy metals in the specimens was determined. Parameters related to fish consumption, such as food safety and health risks, were calculated. In descending order, the average heavy metal concentrations in the fish followed the trend: Zn>Cu>Pb>Cr>Cd>Hg. Moreover, some species of fish have concentrations of Cd and Pb that exceed food safety standards. The concentration of distinct heavy metals varied widely, but the total concentration trended as follows: predatory, omnivorous > filter > herbivorous, benthic > pelagic fish. The hazard quotient and hazard index values were < 1 for all trophic levels of fish, suggesting that consuming the muscle from fish retrieved from Dongting Lake may not present a potential human health risk to adults in terms of heavy metal contamination. Nevertheless, we recommend that Cyprinus carpio, Carassius auratus, and Silurus asotus should be consumed less, and that pollution prevention and control measures should be implemented to reduce Pb, Cd and Cr pollution.

Isolation and identification of a megalocytivirus strain (SKIV-TJ) from cultured spotted knifejaw (Oplegnathus punctatus) in China and its pathogenicity analysis

The spotted knifejaw (Oplegnathus punctatus) has recently emerged as a highly economically significant farmed fish in China. However, due to increasing environmental pollution and breeding density, a range of infectious diseases, including the iridovirus pathogen, have begun to spread widely. In this study, we isolated and identified a strain of Megalocytivirus, SKIV-TJ, from cultured spotted knifejaw in Tianjin, China. We observed significant cytopathic effects (CPE) in SKIV-TJ-infected spotted knifejaw brain (SKB) cells, and electron microscopy showed numerous virus particles in the cytoplasm of SKB cells 6 days post-infection. The annotated complete genome of SKIV-TJ (GenBank accession number ON075463) contained 112,489 bp and 132 open reading frames. Based on the multigene association evolutionary tree using 26 iridovirus core genes, SKIV-TJ was found to be most closely related to Rock bream iridovirus (RBIV). Cumulative mortality of spotted knifejaw infected with SKIV-TJ reached 100% by day 9. A transcriptomic analysis were conducted and a total of 5517 differentially expressed genes were identified, including 2757 upregulated genes and 2760 downregulated genes. The upregulated genes were associated with viral infection and immune signaling pathways. Our findings provide a valuable genetic resource and a deeper understanding of the immune response to SKIV infection in spotted knifejaw.

Vibrio harveyi co-infected with Cryptocaryon irritans to orange-spotted groupers Epinephelus coioides.

The orange-spotted grouper (Epinephelus coioides) is a high economic value aquacultural fish in China, however, it often suffers from the outbreak of parasitic ciliate Cryptocaryon irritans as well as bacterium Vibrio harveyi which bring great loss in grouper farming. In the present study, we established a high dose C. irritans local-infected model which caused the mortality of groupers which showed low vitality and histopathological analysis demonstrated inflammatory response and degeneration in infected skin, gill and liver. In addition, gene expression of inflammatory cytokines was detected to assist the estimate of inflammatory response. Furthermore, we also found that the activity of Na+/K+ ATPase in gill was decreased in groupers infected C. irritans and the concentration of Na+/Cl- in blood were varied. Base on the morbidity symptom occurring in noninfected organs, we hypothesized that the result of morbidity and mortality were due to secondary bacterial infection post parasitism of C. irritans. Moreover, four strains of bacteria were isolated from the infected site skin and liver of local-infected groupers which were identified as V. harveyi in accordance of phenotypic traits, biochemical characterization and molecular analysis of 16S rDNA genes, housekeeping genes (gyrB and cpn60) and species-specific gene Vhhp2. Regression tests of injecting the isolated strain V. harveyi has showed high pathogenicity to groupers. In conclusion, these findings provide the evidence of coinfections with C. irritans and V. harveyi in orange-spotted grouper.

Oxygen-Sensing Protein Cysteamine Dioxygenase from Mandarin Fish Involved in the Arg/N-Degron Pathway and Siniperca chuatsi Rhabdovirus Infection.

Mammalia cysteamine (2-aminoethanethiol) dioxygenase (ADO) controls the stability of the regulator of G protein signaling 4 (RGS4) through the Cys branch of the Arg/N-degron pathway, thereby affecting the response of the body to hypoxia. However, the oxygen-sensing function of ADO remains unknown in teleost fish. Mandarin fish (Siniperca chuatsi) is one of the most important freshwater economic fishes in China. As the scale of the rearing density continues to increase, hypoxia has become an important factor threatening the growth of mandarin fish. Herein, the molecular characterization, the oxygen-sensing enzyme function, and the role in virus infection of ADO from mandarin fish (scADO) were explored. Bioinformation analysis results showed that scADO had all the molecular foundations for achieving thiol dioxygenase function: three histidine residues coordinated with Fe(II), PCO/ADO domain, and a "jelly roll" β-barrel structure. The expression pattern analysis showed that scAdo was highly expressed in the immune-related tissues, liver, and kidneys and responded to hypoxia on the expression level. Protein degradation experiment results revealed that scADO could lead to the degradation of RGS4 protein through the Cys branch of the Arg/N-degron pathway. Furthermore, the expression levels of scADO responded to fish virus infection. scADO could significantly promote the replication of Siniperca chuatsi rhabdovirus, and this was associated with its thiol dioxygenase activity. These findings not only demonstrate scADO as an oxygen-sensing protein in teleost fish, but are also of considerable importance for clarifying the contribution of the mechanism of hypoxia to the outbreaks of fish viruses.

Genome-Wide RADseq Reveals Genetic Differentiation of Wild and Cultured Populations of Large Yellow Croaker.

Larimichthys crocea (also known as the large yellow croaker) is one of the most economically important marine fishes in China, and research on the ecology and genetics of this species is of immense significance. In this study, we performed restriction site-associated DNA sequencing (RAD-seq) of 54 individuals collected from four sites in China to analyze the genetic structure and diversity of large yellow croaker at the genome level. It revealed that the large yellow croaker populations in the Ningde and Zhoushan coastal waters can be clearly distinguished. Different genetic diversity indices were used to analyze the genetic diversity of the large yellow croaker, which showed that there was a differentiation trend between the wild and farmed populations in Ningde. Moreover, we identified genetically differentiated genomic regions between the populations. GO gene enrichment analysis identified genes that are related to fatty acid metabolism and growth. These findings enhance our understanding of genetic differentiation and adaptation to different living environments, providing a theoretical basis for the preservation and restoration of the genetic resources of the large yellow croaker.

Development and characterization of a spleen cell line from yellowfin seabream Acanthopagrus latus and its susceptibility to Mandarinfish ranavirus.

Yellowfin seabream (Acanthopagrus latus) is one of the most commercially important marine fish in China. In this study, a new continuous cell line, named ALS cells, was developed from the spleen tissue of A. latus. The cell line was maintained in Dulbecco's modified Eagle medium/Nutrient Mixture F-12 Ham (DMEM/F-12) supplemented with 10% fetal bovine serum (FBS) and successfully cultured up to 50 passages. The cell line was authenticated by amplifying and sequencing mitochondrial cytochrome C oxidase subunit-I (coi-I) gene. The ALS cell line had the maximum growth rate in DMEM/F-12 medium containing 20% FBS at 27°C. Chromosome number analysis showed that the ALS cells have a modal diploid chromosome number of 34. The ALS cell line was transfected with the pEGFP-N1 plasmid, and green fluorescence was observed. The ALS cell line was used for testing Mandarinfish ranavirus (MRV) susceptibility, and the cytopathic effects in the cell line were observed at 4 days post-infection (dpi). Furthermore, the susceptibility of the ALS cell line to MRV and the levels of MRV mRNA and viral loads were found to be significantly increased at 1-7 dpi. This study revealed that the ALS cell line could be useful for molecular, virological, and biotechnological studies on yellowfin seabream.

Change to the transcriptomic profile, oxidative stress, apoptotic and immunity in the liver of small yellow croaker (Larimichthys polyactis) under hypoxic stress

The small yellow croaker (Larimichthys polyactis) is one of the most highly cultured fish in China, contributing considerably to the country's economy. However, conditions experienced under high-density culture make the fish susceptible to hypoxia, which impacts growth and consequently product quality. To understand the effects of hypoxia stress on physiological and biochemical responses of L. polyactis, we subjected the fish to hypoxic (2.5 mg/L) stress for 96 h. We observed histological changes in the liver pre- and post-hypoxia and measured the changes in liver injury parameters. The results showed injury to the liver of L. polyactis following hypoxic stress, indicating that the liver is an important organ in the hypoxic stress response. To explore the genes and biological processes involved in hypoxic adaptation of L. polyactis at the overall transcription level, liver tissues were obtained pre- (0 h) and post- (6, 24, 48, and 96 h) hypoxia for transcriptomic analysis. GO and KEGG enrichment analysis of differentially expressed genes (DEGs) showed that DEGs were mainly enriched in redox equilibrium, metabolism, immunity, and apoptosis pathways under hypoxic stress. In addition, we examined the changes in molecular indices related to oxidative stress, cell apoptosis, and non-specific immunity in L. polyactis under hypoxic stress. The results showed that hypoxia induced reactive oxygen species overproduction, altered the activity of oxidase (MDA, PCO, 8-OhdG) and antioxidant enzymes (T-AOC, SOD, CAT, GPx, GR), and reduced the mRNA expression of key antioxidant genes (sod1, sod2, cat) in the liver, thus confirming that hypoxic stress induced oxidative stress. Additionally, we confirmed that hypoxic stress induced apoptosis in the liver by inducing the enzyme activity of Caspase-3/8/9 and the mRNA expression of key apoptotic genes (bcl2, bax, fas, and bnip3). Furthermore, hypoxic stress inhibited the activity of non-specific enzymes (AKP, ACP, and LZM) and mRNA expression of immune-related genes (tnf-α, il-1β, and il-17c); hence, hypoxic stress inhibited the non-specific immune function of L. polyactis. In conclusion, our study provides new insights into the molecular mechanisms underlying hypoxia adaptation in marine fish, which will aid in selective breeding of hypoxia-tolerant L. polyactis.

The complete mitochondrial genome and the transfer RNA gene rearrangement of Sillago sinica (Perciformes, Sillaginidae), with reference to the evolution of related species

In this study, the complete mitochondrial DNA sequence of Sillago sinica, a new member of Sillaginidae fishes in China, was obtained by conventional long-PCR amplification. The length of assembled mitogenome sequence was 16,572 bp, containing 13 protein-coding genes, 2 ribosomal RNAs, 22 transfer RNA genes, together with a control region and L-strand replication region just identical to typical bony fishes. An infrequent transfer RNA gene rearrangement event was observed between tRNA-Asn and tRNA-Ala genes that might result from gene sliding. The average genetic distance among 9 Sillago fishes was calculated to be 0.2631, with the least genetic variation between S. sinica and S. aeolus. ML phylogenetic tree constructed based on 13 protein-coding genes also implied the closest relationships between the two. The results provided insight into the mtDNA gene arrangement feature of S. sinica and lay the foundation for further genetic studies on Sillaginidae.

Comparative study of transcriptome profiles in the eyes and brain of the tiger puffer Takifugu rubripes brooder under red light filtered LED

Light spectrum is an important environmental factor affecting fish activities. However, the existing studies on spectrum are usually conducted under monochromatic light, which are multiple variables compared to the natural light conditions and increase uncertainty. The results may be caused by the absence of all other chromatic lights. The tiger puffer Takifugu rubripes is an important commercial marine fish in China, Japan, and Korea. In this study, the effects of red light on the eyes and brain of T. rubripes brooder, including histological changes in retina and optic tectum, the levels of oxidative stress indicators in serum, and changes in gene expression at transcriptome level were examined, after the treatment of full spectrum LED (Fs) and red light filtered LED (Rf) for 52 days. The results showed that the growth and histological structure of retina and optic tectum were not significantly altered. While, Rf significantly decreased the activity of superoxide dismutase and catalase, and increased the content of cortisol (P < 0.05), but had no effect on the levels of glutathione peroxidase and malondialdehyde. Transcriptome data revealed that there were 147 differentially expressed genes (DEGs) in the eyes of Rf vs Fs. Many DEGs related to vision changed significantly. KEGG enrichment and GSEA analyses showed that the significantly enriched arachidonic acid pathway down-regulated in the Rf group, in which genes related to sexual maturation and ovulation presented significant changes, suggesting that Rf may affect the ovulation process through this pathway. In the brain, the number of DEGs was only 20, which are most correlated with circadian rhythm. The present study displayed for the first time the role of red light in promoting ovulation in mature fish by filtering it, which may provide more supports to highlight the function of red light in fish culture.